1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus and a developing method thereof. More particularly, the present invention relates to an electrophotographic image forming apparatus that can minimize or prevent toner dispersion by employing an anti-toner-dispersion element that collects the toner dispersed during a developing process, and a developing method thereof.
2. Description of the Related Art
Electrophotographic image forming apparatuses such as copy machines, printers, facsimiles, and multi-function printers develop a toner image by supplying toner to an electrostatic latent image on an image carrier body which is formed from a digital image signal.
FIG. 1 shows a conventional electrophotographic image forming apparatus, which includes an image carrier body 1, a developing roller 2, a charging unit 5, and an exposing unit 7.
The charging unit 5 contacts one side of the image carrier body 1, and the developing roller 2 faces another side of the image carrier body 1. Light is exposed onto the outer circumferential surface of the image carrier body 1 between the developing roller 2 and the charging unit 5 using a laser beam irradiated by the exposing unit 7.
The outer circumferential surface of the image carrier body 1 is charged to a uniform electric potential by the charging unit 5, and is then exposed to the laser beam irradiated by the exposing unit 7 in response to a digital image signal to form an electrostatic latent image. As the image carrier body 1 rotates, the electrostatic latent image formed on the image carrier body 1 moves towards the developing roller 2. As the electrostatic latent image moves to the closest position between the image carrier body 1 and the developing roller 2, some toner of a toner layer formed on the developing roller 2 moves onto the electrostatic latent image by an electrostatic force so that the electrostatic latent image is developed as a toner image. The developed toner image is transferred and printed onto a recording medium, while the image carrier body 1 rotates.
As the printing speed becomes higher, the developing roller 2 rotates faster. This may disperse toner during a developing process by centrifugal force due to the rotation of the developing roller 2 or by an air current generated by the rotation of the image carrier body 1 or the developing roller 2. The dispersed toner may contaminate the inside of a developing unit containing the developing roller 2 and the image forming apparatus, or may contaminate a non-image portion of the image carrier body 1 if the toner is dispersed between an exposing section and a developing section of the image carrier body 1. In particular, since the toner may not be sufficiently charged due to high speed printing, more reverse polarity toner is present in the toner layer formed on the developing roller 2, and the reverse polarity toner is attached to the non-image portion of the image carrier body 1. As a result, the reverse polarity toner contaminates the non-image portion and remains intact during the developing process, which leads to image contamination.
Accordingly, there is a need for an improved electrophotographic image forming apparatus which minimizes toner dispersion.